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Repair Kopitiam Circuit Breaker Training

By: Yeo Kheng Meng (yeokm1@gmail.com)https://github.com/yeokm1/repair-kopitiam-training-and-equipment

http://yeokhengmeng.com/2016/05/repair-kopitiam-speciality-electrical-tools/For Repair Kopitiam Training

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Inside the 3-pin mains plug (BS1363)EarthYellow/Green• Connects to appliance’s external case, protects user from electric shock

NeutralBlue/Black• Completes the circuit to generator• Tied to ground at power distribution box to ensure stable 0V

LiveBrown/Red• Source of power

Fuse• Blows on overcurrent• Usually 13A

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Earth connections: Normal operation

Kettle

Mains Neutral

Earth

240V

AC ~

Mains Live

Mains Earth

Fuse

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Live wire touches case

Kettle

Mains Neutral

240V

AC ~

Mains Earth

Mains Live FuseX

Earth

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What if there is no Earth wire?

Kettle

Mains Neutral

240V

AC ~

Mains Live Fuse

• Fuse does not blow due to human-body resistance

Earth

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Circuit Breakers

MCB RCCB

Miniature Circuit Breakers (MCBs)• What it does?

• Breaks the circuit on overcurrent eg. short circuit

Residual Current Circuit Breaker (RCCB)• What it does? Breaks the circuit on earth fault• Cause: Current leakage via Earth wire or

human electrocution• When?: Breaks when current difference

between live neutral > threshold (usually 30mA)

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Circuit breaker arrangement

Kettle

Mains Neutral

240V

AC ~

Mains Live

Earth

Mains Earth

RCCB

MCB

Residual Current Circuit Breaker (RCCB)• What it does? Breaks the circuit on earth fault• Cause: Current leakage via Earth wire or

human electrocution• When?: Breaks when current difference

between live neutral > threshold (usually 30mA)

Miniature Circuit Breakers (MCBs)• What it does?

• Breaks the circuit on overcurrent eg. short circuit

Fuse

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Residual Current Circuit Breaker with Overload Protection (RCBO)

Kettle

Mains Neutral

240V

AC ~

Mains Live

Earth

Mains Earth

RCBO

Fuse

• RCBO = RCCB + MCB

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Blackout recovery procedure

• Why? Overcurrent or earth-leakage detected1. Turn off every electrical device2. Flip breaker to ON3. Turn on ONE device at a time. If it trips again, you have found your spoilt device.

• Prioritise simple devices like lamps/ovens. • Computers and refrigerators are sensitive to repeated power cycles.

4. Unplug that spoilt appliance5. Flip breaker back on.

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Problems1. Safety2. Inaccessible onsite breaker3. Inconvenience of breaker trip

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Problem 1: Safety

• Typical I n△ = 30ma threshold for earth leakage• Balance between safety and nuisance trips• But RK always deals with high-risk faulty appliances…

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Problem 2: Inaccessible onsite breaker• Circuit breaker inside locked electrical room• Access to electrical room requires calling

Essential Maintenance Service Unit (EMSU)• 75 mins response time

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Problem 3: Inconvenience of breaker trip• Breaker trips affect the work of others• Eg. Those using sewing machines and welding

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Jurong Setup

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10ma-rcbo-and-anti-external-cb-trip

• Increased safety due to more sensitive 10mA trip rating• Isolates earth trips to this device, onsite breaker does not trip• Read instructions and test before use• Demo video: https://www.youtube.com/watch?v=h-DokWP5Kic

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RCBO trip status

Earth trip: Switch and blue tab is down Overload trip: Only switch is down

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anti-trip-earth-leakage-detector

• Shows blue LED on earth fault without breaker trip• Does not interrupt the work of others• Preserves lifespan of RCBO

• Upstream must have 10mA RCBO• Familiarise with usage instructions beforehand• Demo video: https://www.youtube.com/watch?v=tSpie7baYFM

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Tampines Setup

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10ma-rcbo-mcb-and-anti-external-cb-trip

• Increased safety due to more sensitive 10mA trip rating• Isolates earth trips to this device, onsite breaker does not trip• Extra MCB to increase chances of “catching” overcurrent• Read instructions and test before use

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Bypass B6 MCB switch

Blow marginNo blow margin

No trip margin

0A 9A

May trip

13A 15A

Sure trip margin

Blowing range of Type B: 3 – 5 times rated current, but can trip at 50% of rated current under prolonged use6A x (3 to 5) x 50% = 9A to 15A

13AFuse

Type B6A MCB

Temporarily turn on Bypass Switch if you encounter high power appliances

How?

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Setup is not fool proof!1. There is an Earth-leakage via means other than the Earth

wire2. There is an overload in the circuit eg short circuit.

• Overload Trip sensitivity of external breaker better than ours

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General order of diagnosisAdvise participant about warranty. Then ask what is wrong, specifically if their breaker trips

Connect to main power and try to power on

Check fuse for continuity

Dismantle part of appliance to reach the other end of power cable and test entire cable for continuity

No trip

Diagnose component by component till you find

the fault or give up

RCCB trips

No Power

No Power

If “anti-trip-earth-leakage-detector” is available, use it to determine if earth fault exists.Try to locate any short to Earth wire. Dismantle appliance if needed.